What's Mortons saying ,and I get it ,is that the breeds most popular today ,fell type and pats were originally bred in the lakes of the borders and the north used to bolt or kill foxes in rocks .Since they were adopted down south a bulkier harder more bully type is favoured rather than a lithe bolter capable of despacthing a fox in rocks having first got to it .I agree that many of today's terriers are more boned than I've seen pictures of but I would also argue that it was the breeders of those lithe types that help breed away from type by adding bull all those years ago .